This invention relates to a variable capacity type compressor which is adapted to vary its capacity by changing the compressor starting timing, and more particularly to a variable capacity type compressor which has reduced resistance against the rotation of the rotor at partial capacity operation.
Conventionally, variable capacity type compressors for use in air conditioning systems have been proposed by U.S. Pat. Nos. 4,813,854 and 4,815,945.
These proposed compressors are both constructed such that a control plate member (control element) is disposed for rotation about an axis thereof in opposite directions, which has an outer peripheral edge thereof formed with at least one cut-out portion through which part of refrigerant gas drawn into the cylinder through the inlet port is allowed to leak into a zone under lower pressure, whereby as the control plate member is rotated, the compression starting timing is varied to vary the delivery quantity or capacity. The cut-out portion of the control plate member comprises first and second portions with different depths, the second portion with the smaller depth being disposed such that its upstream end with respect to the direction of rotation of the rotor is positioned upstream of an upstream end of the inlet port when the control plate member is circumferentially displaced to an extreme position in which the minimum capacity of the compressor is obtained, to thereby eliminate unnecessary compression and hence resistance of the compressed gas to the rotation of the rotor, which would be caused if the cut-out portion has the same depth along its whole length as in a conventional variable capacity type compressor during minimum capacity operation.
More specifically, as shown in FIGS. 1 and 2, the proposed compressors each comprise a cylinder formed by a cam ring 100 with an oblong camming inner peripheral surface 100a, and a pair of side blocks, not shown, closing opposite ends of the cam ring 100, a rotor 101 rotatably received within the cylinder, a pair of compression spaces 102 defined between the cylinder and the rotor 101, vanes 103.sub.1 -103.sub.5 radially movably carried by the rotor 101, and a control plate member 105 fitted in an annular recess 104 formed in an end face of one of the side blocks facing the rotor 101 for rotation about its own axis between a full capacity extreme position and a minimum capacity extreme position to vary the compression starting timing. The control plate member 15 has its outer peripheral edge formed with two cut-out portions 107 circumferentially extending at diametrically opposite locations through which refrigerant gas is drawn into the compression spaces 102 through respective inlet ports 106 formed in the one side block, over the entire rotatable angle range of the control plate member 105. Each cut-out portion 107, of which a downstream end 107a with respect to the direction of rotation of the rotor determines the compression starting timing, comprises a first portion 107.sub.1 extending from the downstream end 107a and terminating at a circumferentially intermediate point of the cut-out portion 107 and being almost flush with the outer peripheral surface of the rotor 101, and a second portion 107.sub.2 extending continuously from the first portion 107.sub.1 to an upstream end 107b with respect to the direction of rotation of the rotor and being located radially outwardly of the outer peripheral surface of the rotor 101 by a predetermined amount.
However, according to these compressors, when the control plate member 105 is in the minimum capacity extreme position or in the vicinity thereof, refrigerant is allowed to flow into a compression chamber A defined between vanes 103.sub.2 and 103.sub.3 which has started a suction stroke from a immediately preceding compression chamber B defined between vanes 103.sub.1 and 103.sub.2 along one lateral side wall of the vane 103.sub.2 and then through a small gap X (hatched in FIG. 3) defined between the vane 103.sub.2, the upstream end 107b of the cut-out portion 107, and the camming inner peripheral surface 100a of the cylinder, as shown by the arrow in the figure. Thus, refrigerant is drawn into the compression chamber A which has just started the suction stroke, at such a small rate that high negative pressure is developed in the compression chamber A. As a result, large torque Y is created and acts upon the vane 103.sub.2 in a reverse direction to the direction of rotation of the rotor 101 to resist against the rotor rotation.